To better understand the background and problems faced by those of skill in this area of technology it is useful to understand the basic workings of the heart and circulatory system. The following discussion refers to schematics of the heart shown in FIGS. 1 and 2.
The human heart is a muscular pump having four separate cavities and a series of valves allowing blood to pass in one direction only. Mammals, including humans, have a double circulatory system. Blood that has released oxygen to the tissues (9 and 14) and has absorbed carbon dioxide from them (venous blood) is returned to the heart through the superior and the inferior venae cavae (11 and 10). This blood enters the right auricle (3), whose contractions cause the blood to pass through the tricuspid valve (16) in the right ventricle (1). The contractions of the right ventricle pass the blood through the pulmonary semilunar valves (17) and along the two pulmonary arteries (5) into the lungs (6). In the lungs, the blood is oxygenated and returns to the heart through the pulmonary veins (7) and thus enters the left auricle (4). This chamber contracts and passes the blood through the bicuspid, or mitral, valve (15) into the left ventricle (2), whose contractions force the blood through the aortic semilunar valve (18) into the aorta (12 and 13), which is the biggest artery of the body and to other parts of the body through, i.a., the great arteries 8.
Thus the right side of the heart serves mainly to pump deoxygenated blood through the lungs, while the left side pumps oxygenated blood throughout the rest of the body. This is represented as a flow schematic in FIG. 2, where similar numbers refer to similar parts of the heart. The heart varies the output by varying the volume of blood admitted into the ventricles each time the latter are filled and also by varying the rate of contraction (faster or slower heartbeat). The left side of the heart (left auricle and ventricle) has to circulate the blood through all parts of the body, except the lungs, and has thicker and more strongly muscular walls than the right side, which has to perform the pulmonary blood circulation only. For proper functioning, the left side and the right side must be accurately interadjusted, both with regard to the contraction rate of the respective chambers and with regard to the output of blood. When functional disorders of the heart occur, it may be necessary to examine the heart to determine the problem and possibly perform surgery or provide treatment.
In performing examinations or treatments of a subject's heart, or performing surgery on the heart, it is often necessary to reduce the rate at which it normally beats or stop its beating completely. This allows a physician to observe, or operate on, the heart more easily. However, by reducing or stopping the heart rate (i.e. cardioplegia), blood will not be adequately circulated to the rest of the body. Thus, it is generally necessary to circulate the blood using some type of extracorporeal blood circulating means that regularly circulates oxygen-rich blood through the arteries, collects oxygen-depleted blood returning through the veins, enriches the oxygen-depleted blood with additional oxygen, then again circulates the oxygen-rich blood.
The types of examinations, treatments and operations that require some degree of cardioplegia or drug delivery and extracorporeal blood circulation include open heart surgery and less-invasive heart surgery to perform single or multiple coronary artery bypass operations, correct malfunctioning valves, etc. Others include, but are not limited to, myocardial revascularization, balloon angioplasty, correction of congenital defects, surgery of the thoracic aorta and great vessels, and neurosurgical procedures.
The extracorporeal blood circulation generally requires the use of some type of heart-lung machine, i.e. a cardiopulmonary machine. This has the threefold function of keeping the replacement blood in circulation by means of a pumping system, of enriching with fresh oxygen the blood of low oxygen content coming from the patient's body, and regulation of patient temperature. The system shown in FIG. 3 diagrammatically describes the manner in which such a machine works.
The venous blood, before it enters the right auricle of the heart is diverted into plastic tubes (20), generally by gravity flow. The tubes are positioned to receive the blood from the superior and inferior venae cavae (shown as 11 and 10 in FIG. 1). This blood, which has circulated through the body and consequently has a low oxygen content is collected in a reservoir (21). A blood pump (22) is used to pump the blood through a heat exchanger (23) and artificial lung (24). The heat exchanger (23) and artificial lung (24) may be one of several designs to regulate blood temperature and increase the oxygen content of the blood. Modern designs use advanced membrane technology to achieve the oxygenation, which is similar to the way red blood cells absorb oxygen from the human lung. The oxygenated blood then passes through a filter (25) and is returned to the patient. Losses of blood occurring during the course of the operation are compensated by an additional blood reservoir (26). Collected blood is passed through a defoamer (27) and is likewise passed to the to the reservoir 21, heat exchanger (23) and artificial lung (24). Before starting the cardiopulmonary bypass machine the extracorporeal circuit is filled with one or two liters of saline solution.
In circulating the oxygenated blood to the body from filter 25, it can be pumped through a catheter 28 by inserting the catheter into the aorta or one of its major branches and pumping the blood through the catheter. However, when the heart is to be operated on, it must be free of blood and sometimes the heart beat must be reduced or stopped completely. Referring again to FIG. 1, blood is prevented from entering the heart by blocking the ascending aorta 12 near the semilunar valve 18 while at the same time preventing blood from entering the right auricle 3 by withdrawing blood through the superior vena cavae 11 and inferior vena cavae and 10. Blocking the ascending aorta may be achieved by clamping or preferably by balloon blockage. At the same time that blood is prevented from flowing through the heart, a cardioplegia solution is administered locally to the heart to arrest the heart. Thus, there is a need for a device that allows a heart specialist to locally administer cardioplegia to the heart, block the flow of blood to the heart, while at the same time circulating oxygenated blood to the patient's body, particularly through the great arteries (8 in FIG. 1), to ensure all limbs and tissues remain undamaged during the heart examination or operation.
Several devices are described in the literature to address the need for an appropriate device. One example is disclosed in U.S. Pat. No. 5,312,344 issued 17 May 1994 to Grinfeld et al. This patent describes a multichannel catheter having at least three passageways, one of which is used for blood circulation and another is used for cardioplegia transportation. The third is used to transport fluid to an inflatable balloon which is located at the distal end of the catheter and is used to block the ascending aorta. The channel for blood is described as having outlets on the downstream side of the balloon to allow blood to be circulated to the body tissues. The design of this multichannel catheter shows that either each passageway is a tube encased in a cannula or the smaller passageways are located within the larger passageway for cardioplegia solution or blood. Thus, the small passageways are not integral with the walls of the blood-carrying tube. Also, there is no teaching of the importance of the large volume needed for the blood-carrying catheter.
Another example can be seen in U.S. Pat. No. 5,433,700 issued 18 Jul. 1995 to Peters. This patent describes a process for inducing cardioplegic arrest of a heart which comprises maintaining the patient's systemic circulation by peripheral cardiopulmonary bypass, occluding the ascending aorta through a percutaneously placed arterial balloon catheter, venting the left side of the heart, and introducing a cardioplegia agent into the coronary circulation. As part of the disclosure a multichannel catheter is disclosed which provides channels for the cardioplegia solution, a fluid transportation to inflate the balloon and a lumina for instrumentation. However, there is no description in the patent of a multichannel catheter which is designed to administer cardioplegia solution, inflate a balloon, and provide circulation of blood all using the same multichannel catheter. The Peters process teaches the use of a separate catheter to deliver oxygenated blood to the body while a heart is stopped.
Another example of a device is found in U.S. Pat. No. 5,478,309 issued 26 Dec. 1995 to Sweezer et al. This is a rather complex device and system of venous perfusion and arterial perfusion catheters for use in obtaining total cardiopulmonary bypass support and isolation of the heart during the performance of heart surgery. One of the multichannel catheters described in the patent for delivering cardioplegia solution to the heart while blocking the ascending aorta and circulating perfused blood. This catheter requires a cannula having two passageways therethrough. In the first passageway another slidable cannula having two passageways through it and having a passageways for guidewires are positioned. These passageways are for delivering a fluid for inflating the balloon at the distal end of the catheter and cardioplegia solution to the heart to stop its beating. The second passageway through the cannula used for transporting blood that has been oxygenated by the cardiopulmonary machine. However in this particular design no discussion of the need to maximize the flow of blood and minimize the damage to the blood components is discussed. Thus the volume of the two passageways is about the same.
Another device is described in U.S. Pat. No. 5,458,574 issued 17 Oct. 1995 to Machold et al. It shows a multichannel catheter which has channels for fluid to blow up balloons for blocking the aorta, a channel for cardioplegia solution and a channel for instruments for examining the heart. Nothing in the patent describes a multichannel catheter of applicant's design.
Still another patent, U.S. Pat. No. 5,452,733 issued 26 Sep. 1995 to Sterman et al. No details are given in that patent of the design of the catheter that might be used.
Still another patent application filed as PCT/US 94/09938 having international publication No. WO95/08364 filed 1 Sep. 1994 in the name of Evard et al. describes an endovascular system for arresting the heart. This too lacks any detailed description of a multichannel catheter that could be used in the manner described in the instant application.
PCT International Application number PCT/U.S. Pat. No. 94/12986 published as Publication No. W095/15192, filed 10 Nov. 1994 in the name of Stevens et al. provides a description of a partitioning device that is coupled to an arterial bypass cannula. The description provides for the cannula to be introduced to the femoral artery where the partitioning device has a balloon at the end of the flexible tube to block the ascending aortic artery and allow blood to circulate through a lumen.
While the above devices address in part the needs of the art, it has been discovered that certain problems exist that must be further addressed to maximize the efficiency of the device and cardiopulmonary operations. The first problem is ensuring maximum flow of blood through the device (which must be of a diameter sufficiently small to fit into a patient's femoral artery) so that the tissues receive enough nourishment (i.e. oxygen, etc.). We have found that by ensuring that (1) the channel for blood is at least 70% of the available volume and (2) the channel for blood is clear of an other tubes or obstructions, the blood flow is maximized. Another problem is ensuring that the blood components are not injured by excess flow rate and sheer stress in the circulation process. We have found that by providing strategically located blood outlets that are preferably elongate in shape the sheer stress is reduced. Another problem is ensuring the blood flow to the great arteries is maximized to avoid damage to the tissues, particularly the brain. We have found tissue damage is avoided by ensuring the blood circulating outlets are located on the catheter such that when the catheter of this invention is in place, the outlets are located adjacent to the great artery openings. Finally we have found that by using extrusion molding techniques the multichannel catheter of this invention is prepared so that (1) the blood-carrying passageway is at least about 70% of the available volume and (2) the other passages account for less than about 30% of the available volume and are integral with the wall of the blood-carrying passageway, the blood flow problems are minimized.